RE: [PATCH V4 07/13] hyperv/Vmbus: Add SNP support for VMbus channel initiate message

[Michael Kelley <mikelley@xxxxxxxxxxxxx>]

From: Tianyu Lan <ltykernel@xxxxxxxxx> Sent: Friday, August 27, 2021 10:21 AM
> 

Subject line tag should be "Drivers: hv: vmbus:"

> The monitor pages in the CHANNELMSG_INITIATE_CONTACT msg are shared
> with host in Isolation VM and so it's necessary to use hvcall to set
> them visible to host. In Isolation VM with AMD SEV SNP, the access
> address should be in the extra space which is above shared gpa
> boundary. So remap these pages into the extra address(pa +
> shared_gpa_boundary).
> 
> Introduce monitor_pages_original[] in the struct vmbus_connection
> to store monitor page virtual address returned by hv_alloc_hyperv_
> zeroed_page() and free monitor page via monitor_pages_original in
> the vmbus_disconnect(). The monitor_pages[] is to used to access
> monitor page and it is initialized to be equal with monitor_pages_
> original. The monitor_pages[] will be overridden in the isolation VM
> with va of extra address.
> 
> Signed-off-by: Tianyu Lan <Tianyu.Lan@xxxxxxxxxxxxx>
> ---
> Change since v3:
>       * Rename monitor_pages_va with monitor_pages_original
>       * free monitor page via monitor_pages_original and
>         monitor_pages is used to access monitor page.
> 
> Change since v1:
>         * Not remap monitor pages in the non-SNP isolation VM.
> ---
>  drivers/hv/connection.c   | 75 ++++++++++++++++++++++++++++++++++++---
>  drivers/hv/hyperv_vmbus.h |  1 +
>  2 files changed, 72 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/hv/connection.c b/drivers/hv/connection.c
> index 6d315c1465e0..9a48d8115c87 100644
> --- a/drivers/hv/connection.c
> +++ b/drivers/hv/connection.c
> @@ -19,6 +19,7 @@
>  #include <linux/vmalloc.h>
>  #include <linux/hyperv.h>
>  #include <linux/export.h>
> +#include <linux/io.h>
>  #include <asm/mshyperv.h>
> 
>  #include "hyperv_vmbus.h"
> @@ -104,6 +105,12 @@ int vmbus_negotiate_version(struct vmbus_channel_msginfo 
> *msginfo, u32 version)
> 
>       msg->monitor_page1 = virt_to_phys(vmbus_connection.monitor_pages[0]);
>       msg->monitor_page2 = virt_to_phys(vmbus_connection.monitor_pages[1]);
> +
> +     if (hv_isolation_type_snp()) {
> +             msg->monitor_page1 += ms_hyperv.shared_gpa_boundary;
> +             msg->monitor_page2 += ms_hyperv.shared_gpa_boundary;
> +     }
> +
>       msg->target_vcpu = hv_cpu_number_to_vp_number(VMBUS_CONNECT_CPU);
> 
>       /*
> @@ -148,6 +155,35 @@ int vmbus_negotiate_version(struct vmbus_channel_msginfo 
> *msginfo, u32 version)
>               return -ECONNREFUSED;
>       }
> 
> +
> +     if (hv_is_isolation_supported()) {
> +             if (hv_isolation_type_snp()) {
> +                     vmbus_connection.monitor_pages[0]
> +                             = memremap(msg->monitor_page1, HV_HYP_PAGE_SIZE,
> +                                        MEMREMAP_WB);
> +                     if (!vmbus_connection.monitor_pages[0])
> +                             return -ENOMEM;
> +
> +                     vmbus_connection.monitor_pages[1]
> +                             = memremap(msg->monitor_page2, HV_HYP_PAGE_SIZE,
> +                                        MEMREMAP_WB);
> +                     if (!vmbus_connection.monitor_pages[1]) {
> +                             memunmap(vmbus_connection.monitor_pages[0]);
> +                             return -ENOMEM;
> +                     }
> +             }
> +
> +             /*
> +              * Set memory host visibility hvcall smears memory
> +              * and so zero monitor pages here.
> +              */
> +             memset(vmbus_connection.monitor_pages[0], 0x00,
> +                    HV_HYP_PAGE_SIZE);
> +             memset(vmbus_connection.monitor_pages[1], 0x00,
> +                    HV_HYP_PAGE_SIZE);
> +
> +     }

I still find it somewhat confusing to have the handling of the
shared_gpa_boundary and memory mapping in the function for
negotiating the VMbus version.  I think the code works as written,
but it would seem cleaner and easier to understand to precompute
the physical addresses and do all the mapping and memory zero'ing
in a single place in vmbus_connect().  Then the negotiate version
function can focus on doing only the version negotiation.

> +
>       return ret;
>  }
> 
> @@ -159,6 +195,7 @@ int vmbus_connect(void)
>       struct vmbus_channel_msginfo *msginfo = NULL;
>       int i, ret = 0;
>       __u32 version;
> +     u64 pfn[2];
> 
>       /* Initialize the vmbus connection */
>       vmbus_connection.conn_state = CONNECTING;
> @@ -216,6 +253,21 @@ int vmbus_connect(void)
>               goto cleanup;
>       }
> 
> +     vmbus_connection.monitor_pages_original[0]
> +             = vmbus_connection.monitor_pages[0];
> +     vmbus_connection.monitor_pages_original[1]
> +             = vmbus_connection.monitor_pages[1];
> +
> +     if (hv_is_isolation_supported()) {
> +             pfn[0] = virt_to_hvpfn(vmbus_connection.monitor_pages[0]);
> +             pfn[1] = virt_to_hvpfn(vmbus_connection.monitor_pages[1]);
> +             if (hv_mark_gpa_visibility(2, pfn,
> +                             VMBUS_PAGE_VISIBLE_READ_WRITE)) {

In Patch 4 of this series, host visibility for the specified buffer is done
by calling set_memory_decrypted()/set_memory_encrypted().  Could
the same be done here?   The code would be more consistent overall
with better encapsulation.  hv_mark_gpa_visibility() would not need to
be exported or need an ARM64 stub.

set_memory_decrypted()/encrypted() seem to be the primary functions
that should be used for this purpose, and they have already have the
appropriate stubs for architectures that don't support memory encryption.

> +                     ret = -EFAULT;
> +                     goto cleanup;
> +             }
> +     }
> +
>       msginfo = kzalloc(sizeof(*msginfo) +
>                         sizeof(struct vmbus_channel_initiate_contact),
>                         GFP_KERNEL);
> @@ -284,6 +336,8 @@ int vmbus_connect(void)
> 
>  void vmbus_disconnect(void)
>  {
> +     u64 pfn[2];
> +
>       /*
>        * First send the unload request to the host.
>        */
> @@ -303,10 +357,23 @@ void vmbus_disconnect(void)
>               vmbus_connection.int_page = NULL;
>       }
> 
> -     hv_free_hyperv_page((unsigned long)vmbus_connection.monitor_pages[0]);
> -     hv_free_hyperv_page((unsigned long)vmbus_connection.monitor_pages[1]);
> -     vmbus_connection.monitor_pages[0] = NULL;
> -     vmbus_connection.monitor_pages[1] = NULL;
> +     if (hv_is_isolation_supported()) {
> +             memunmap(vmbus_connection.monitor_pages[0]);
> +             memunmap(vmbus_connection.monitor_pages[1]);
> +
> +             pfn[0] = virt_to_hvpfn(vmbus_connection.monitor_pages[0]);
> +             pfn[1] = virt_to_hvpfn(vmbus_connection.monitor_pages[1]);
> +             hv_mark_gpa_visibility(2, pfn, VMBUS_PAGE_NOT_VISIBLE);

Same comment about using set_memory_encrypted() instead.

> +     }
> +
> +     hv_free_hyperv_page((unsigned long)
> +             vmbus_connection.monitor_pages_original[0]);
> +     hv_free_hyperv_page((unsigned long)
> +             vmbus_connection.monitor_pages_original[1]);
> +     vmbus_connection.monitor_pages_original[0] =
> +             vmbus_connection.monitor_pages[0] = NULL;
> +     vmbus_connection.monitor_pages_original[1] =
> +             vmbus_connection.monitor_pages[1] = NULL;
>  }
> 
>  /*
> diff --git a/drivers/hv/hyperv_vmbus.h b/drivers/hv/hyperv_vmbus.h
> index 42f3d9d123a1..7cb11ef694da 100644
> --- a/drivers/hv/hyperv_vmbus.h
> +++ b/drivers/hv/hyperv_vmbus.h
> @@ -240,6 +240,7 @@ struct vmbus_connection {
>        * is child->parent notification
>        */
>       struct hv_monitor_page *monitor_pages[2];
> +     void *monitor_pages_original[2];
>       struct list_head chn_msg_list;
>       spinlock_t channelmsg_lock;
> 
> --
> 2.25.1